Influenza vaccine in unprimed children: improved immunogenicity with few reactions following one high dose of split-product vaccine.

Thirty-one unprimed children and young adults received an influenza A/USSR/77 vaccine containing 43 microgram of hemagglutinin. Their HAI antibody response was compared to that in 92 age-matched individuals from the 1978 national influenza immunization trial who received 10 and 4 microgram HA vaccines. A dose-related antibody response was observed after the first vaccine doses in the 7- to 12- and 13- to 25-year-old groups. An HAI titer greater than or equal to 40 was present in 81% and 93% of 43 microgram HA recipients, in 38% and 43% of 10 microgram HA recipients, and in 24% and 12% of 4 micrograms HA recipients respectively. The antibody response to the 43 microgram HA dose was significantly higher than was the response to the 10 and 4 microgram HA doses. The local and systemic side effects were not significantly different among the three vaccine groups and the placebo group. Thus, a high dose of influenza A/USSR/77 split-product vaccine given to unprimed children and young adults stimulated presumably protective levels of antibody and was free of a significant incidence of side effects.